Dryness control for dryer



2 Sheets-Sheet 1 Nov. 15, 1966 w. H. GARTLEY ETAL DRYNESS CONTROL FOR DRYER Filed. Feb. 2 1964 A 'I'TORNEYS Nov. 15, 1966 w. H. GARTLEY ETAL 3,284,919

DRYNESS CONTROL FOR DRYER Filed Feb. 1964 2 Sheets-Sheet 2 M W *MWORNEYS United States Patent 3,284,919 DRYNESS CONTROL FOR DRYER William H. Gartley, St. Joseph, and Donald E. Janke,

Benton Harbor, Mich, assignors to Whirlpool Corporation, Benton Harbor, Mich., a corporation of Dela- Ware Filed Feb. 28, 1964, Ser. No. 348,238 Claims. (Cl. 3448) This invention relates to a clothes dryer and more particularly to a clothes dryer dryness measuring and control system which was evolved with the general object of providing a system in which a desired degree of dryness is obtained automatically and with a high degree of reliability despite variations in operating conditions and changes in circuit parameters and other variables. The system of this invention attains such results in a highly efficient and yet inexpensive manner, using a minimum number of component parts.

The illustrated embodiment of the invention is incorporated in a home type clothes dryer but it will be understood that various principles and features of the invention can be applied to other types of material handling systems, the terms clothes and clothes dryer being used herein in a generic sense to include equivalent ma terials and systems.

In this system of this invention, a dryness sensing and timing circuit is used of a type .in which an output signal is produced after a delay which is dependent on the dryness of the materials. This circuit may comprise a capacitor connected through a charging resistance to a voltage source, with a current path through the clothes being provided in shunt relation to the capacitor, and with an output signal being produced when the charge of the capacitor reaches a certain value.

In prior systems, the output signal from such a sensing and timing circuit has been used to deactivate the heating means of the dryer. Such prior systems have been generally satisfactory but have required careful adjustment and have also required that the operating voltages, circuit parameters and other conditions be maintained substantially constant.

According to this invention, a dryness sensing and timing circuit is automatically recycled at least once and the heating means of the dryer is not deactivated until the second or some subsequent output signal from the circuit. With this feature, it is found that the adjustment, operating conditions and parameters of the circuit are not critical and at the same time, the desired degree of dryness of clothes may be obtained automatically despite wide variations in conditions such as the initial moisture content of the clothes, the amount of clothes in the dryer, the type of fabric, ambient temperature and humidity conditions, and the like.

Further important features of the invention reside in a comparatively simple but highly reliable circuit arrangement for obtaining the recycling action.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate a preferred embodiment and in which;

FIGURE 1 is a diagrammatic elevational view of the rear side of a dryer incorporating a dryness control system according to this invention;

FIGURE 2 is a sectional view taken substantially along line IIII of FIGURE 1, illustrating a dryness sensing assembly;

FIGURE 3 is a sectional view taken substantially along line IIIIII of FIGURE 2, illustratingthe mounting of a contacting brush; and

Patented Nov. 15, 1966 FIGURE 4 is an electrical circuit diagram illustrating the recycling circuit arrangement of this invention.

Reference numeral 10 generally designates a clothes dryer incorporating the dryness control system of this invention, wherein the dryness of clothes is sensed by electrical resistance measurement to automatically control energization of drive and heating means. It will be understood that the dryness control system of this invention, and various features thereof, may be applied to dryers of types different from that illustrated.

In the illustrated dryer 10, clothes to be dried are placed with a drum 11 disposed within a casing 12 and journalled for rotation in a bearing assembly 9 about a horizontal axies. To drive the drum 11 and tumble clothes therewithin, a belt 14 is trained about the periphery of the drum and about a pulley 15 driven'by an electric motor 16. For drying the clothes, air enters from the lower portion of the casing 12 and through an nlet opening 18 in a back panel 19 of the casing 12, into a duct 20 having an electric heater 21 therewithin. Heated air from the duct 20 passes through an outlet opening 22 and into the drum 11, through openings in the back wall thereof. The air, after picking up moisture from clothes within the drum, is withdrawn from the drum into the inlet 23 of a blower 24 which discharges through a vent 25 in partial back panel 26 and through a suitable pipe (not shown) to the outside atmosphere. The blower is driven by a pulley 28 driven through a belt 29 from a pulley 30 on the shaft of the motor 16.

The motor 16 and heater 21 are connected to a control unit 32 through cables 33 and 34, the control unit 32 being connected through a Wire 35 to a dryness sensing assembly 36 (FIGURE 4). The invention does not reside in the dryness sensing assembly 36 by itself, but it will be first described in detail, to facilitate an understanding of the recycling feature of this invention, which is described in detail hereinbelow in connection with the electrical circuit diagram of FIGURE 4.

As shown in FIGURE 2, the dryness sensing assembly 36 comprises a pair of spaced bands 37 and 38 of conductive material, preferably stainless steel, mounted within the drum 11 at positions intermediate rows of tumbling baflles 39 and 40. The ring 37 is electrically connected through a wire 41 to the drum 11 which is electrically connected through the drum-support bearings to the casing 12 of the dryer, the casing forming an electrical ground of the system. The ring 38 is connected through a wire 42 to a slip ring 43 of conductive material, preferably stainless steel, on the outside of the drum 11. The ring is engaged by a contactor brush 44 which is connected through the wire 35 to the control unit 32.

As described hereinbelow in connection with the electrical circuit diagram of FIGURE 4, the control unit 32 controls the drive and heating means in response to the electrical resistance presented by the clothes between the rings 37 and 38, as measured between the wire 35 and the casing 12, the electrical resistance being relatively low when the clothes are wet and being increased as the clothes approach the dry state.

To support the slip ring 43 on the drum 11, it is disposed in a groove 47 in the outer surface of a strip 48 of insulating material, preferably an extruded strip of polypropylene material, the strip 48 forming a complete ring about the periphery of the drum. The strip 48 has a groove 49 in its inner surface which engages over a bead 50 on the drum 11, formed by the junction between the edge portion of an outer cylindrical Wall 51 of the drum and the outer peripheral edge portion of a front wall 52 of the drum. The strip 48 additionally has a radially inwardly projecting portion 53 engaging the drum to space an internal surface portion 54 of the strip 48 from the opposed surface of the drum 11. The dimensioning of the parts is such that the strip 48 is stressed against tension in the slip ring 43 to maintain the parts in firm assembly. Assembly of the parts is facilitated by providing a rounded edge 55 on the forward portion of the strip 48.

FIGURE 3 shows the support of the brush 44 which is preferably of a metal graphite material, disposed in a holder 58 which is secured to one end of a spring wire 59 having a coiled portion and having an opposite end secured to a rod 60 of insulating material supported from the casing 12. A copper braided wire 61 extends from the brush holder 58 to a terminal 62, to which the wire 35 is attached.

To support the bands 37 and 38 on the interior of the drum, a strip 64 of insulating material, preferably extruded polypropylene, is provided forming a ring in engagement with the internal surface of the drum 11, intermediate the tumbling bafiles 39 and 40. The strip 64 has a pair of radially inwardly extending annular ribs 65 and 66 with projections 67 and 68 from opposite sides of the ribs 65 and 66 spaced axially inwardly from opposed surface portions of the strip 64 to define annular grooves which receive turned-in edge portions of the bands 37 and 38 to firmly hold the bands in position. The strip 64 is ad-ditionallyformed with a groove 69 projecting inwardly from the outer surface thereof and of generally T-shaped configuration, to receive the heads of a plurality of securing clips 70 which have reduced diameter shank portions projecting through openings in the cylindrical wall 51 of the casing 12, the outer ends of the clips 70 being deformed to lock the same in position after assembly.

The strip 64 has a central portion 72 which is thicker than the side portions thereof to allow for the groove 69 while minimizing the weight and amount of material in the strip. The edges of the portion 72 are preferably rounded, and rounded reinforcing beads 73 and 74 are also provided on the edges of the strip 64.

Referring now to the electrical circuit diagram of FIGURE 5, the circuit and its operation will be first described with reference to what its operation would be without the recycling feature of this invention, to facilitate an understanding of the advantages of the recycling feature.

The motor 16 has a main winding 75 and a starting winding 76 initially connected in parallel through a contact 77 of a centrifugal switch, contact 77 being disconnected from the starting winding 76 and connected to a contact 78 when the motor reaches a certain speed. The common connection of the windings 75 and 76 is connected to a neutral line 79, while the main winding 75 is connected through a conductor 80 and through a normally open contact 81 of a relay 82 to a circuit point 83 which is connected through a door switch 91 to the line terminal 87. The door switch 91 is physically located in such a relation to the drum access door (not shown) so as to be actuated to the closed position upon the closing of the access door and thereby completing the electrical connection to the control circuit. When the door is opened, the door switch 91 opens thereby breaking the electrical circuit and de-energizing the drive motor 16 and thus preventing drum rotation whenever the door is open.

One terminal of an operating coil 96 of the relay 82 is connected to a push-to-start switch 93 through diode 95. Push-to-start switch 93 is a spring biased normally open switch that is momentarily manually actuated to initiate the drying cycle. The other terminal of the coil 96 is connected to the anode of a silicon controlled rectifier 97 having a cathode connected through a resistor 98 to ground and also connected through conductor 99 to the neutral line 79. The silicon controlled rectifier 97 normally has a gate voltage applied thereto through the voltage dropping resistor 117 such as to render it conductive, and the relay coil 96 is thus energized to close the contact 81 and start the motor 16, to also engage a holding contact 100 with a fixed contact 101 and shortcircuit the start switch 93, and to additionally close a contact 102 and connect the line terminal 87 to one terminal of a resistance element 103 in the heater 21, the other terminal of the element 103 being connected to an L line terminal 104.

The silicon controlled rectifier 97 is controlled in response to dryness, to be rendered non-conductive when the resistance presented between the line 35 and ground reaches a certain value. In particular, the cathode terminal of the diode 95 is connected through a diode 106, a resistor 107 and an adjustable resistor 109 to the line 35. Circuit point 108 is connected to a circuit point 111 which is connected through a resistor 112 and a capacitor 113 to the cathode of the silicon controlled rectifier 97, circuit point 111 being also connected through a resistor 114 and a neon lamp 115 to the base of a transistor 116 having its emitter connected to the cathode of the silicon controlled rectifier 97, and having its collector connected to the gate of the silicon controlled rectifier 97, a resistor 117 being connected between the gate and anode of the rectifier 97.

In operation, the capacitor 113 is charged by current flow through the circuit including resistors 112, 109 and 107 and the diode 106. Initially, however, when the clothes are wet, the amount of charge of the capacitor 113 is limited by the low resistance of the shunt circuit from the circuit point 108 to ground through the low resistance 0f the clothes as presented between the line 35 and ground. However, as the clothes dry, the resistance of the shunt circuit increases and ultimately the charge across the capacitor 113 reaches a certain level such as to cause the neon lamp 115 to discharge through the baseemitter circuit of the transistor 116. The transistor 116 then conducts to reduce the voltage of the gate of the silicon controlled rectifier 97 to a value such that it will not conduct during the next half-cycle of voltage applied thereto, only positive half-cycles being applied because of the provision of the diode 95 in the circuit. The rectifier will not conduct as long as the neon lamp 115 is ionized and is conductive which is approximately A: seconds in the present illustration.

When the rectifier 97 ceases to conduct, the relay 96 is deenergized to open the contacts 81 and 102 and moves contact arm 100 to contact 122. The heater 103 is then deenergized, but energization of the motor 16 may be continued through a cool down thermostat 120 connected between the contact 78 of the motor centrifugal switch and the line terminal 87. The thermostat 120 is mounted on the blower 24 and protrudes through a circular opening in the blower wall in order to sense the temperature of the exhaust air flowing therethrough. The thermostat 120 includes a switch which is closed when the dryer is heated to a certain temperature and does not open until the temperature drops below a certain value. Thus the tumbling and blowing operations are continued after deenergization of the heater, until the temperature drops below a certain value.

The resistors 107 and 109 should preferably have a relatively high resistance, to provide a delay action between the attainment of a certain dryness level and the deenergization of the heater. This delay action allows the clothes to become quite dry, while minimizing critical adjustment requirements on the resistance measuring circuit, which might otherwise tend to create a dangerous no shut-off condition. By way of example, the variable resistor 109 may have a selective value of .47 to 27 megohms, the resistor 107 a value of 68,000 ohms, the resistor 112 a value of 22,000 ohms, the resistor 114 a value of 10,000 ohms and the resistor 117 a value of 8,200 ohms. The resistor 98 is provided as a safety precaution in case the dryer terminals are reversed when being connected to the household line to avoid tying the neutral line 79 directly to the cabinet or casing of the dryer, and may preferably have a value of 1 megohm. The capacitor 113 may have a value of 4 microfarads.

To provide a path for the complete discharge of capacitor 113 after neon lamp 115 discharges, circuit point 111 is connected through a resistor 121 to contact 122 of relay 82, through contact arm 100, through diode 95, through relay coil 96, through resistor 117, through the gate of silicon controlled rectifier 97 and through conductor 99 to capacitor 113.

The above described operation of the control explains the operation of the circuit without the incorporation of present invention. The control as described above will perform and determine the end point of the dry cycle, but it has been found during the testing of the sensing and control system that the materials in the drum 11 are not completely dry when the voltage is no longer conducted to ground through the sensing system 36. It is of necessity therefore to provide an additional drying time after the materials within the drum 11 become dry enough to not bleed off the applied voltage to ground. This additional time can be accomplished to some degree by using the appropriate size resistors and capacitor to obtain a relatively long charging time for capacitor 113. The length of time that could be obtained by increasing the charging time by this method was limited by the physical size of the capacitor required and the economics involved therewith and considering the system described above it was possible to obtain a charging time of ap proximately ten minutes. This additional time of ten minutes, as found by testing, did not give a fully dried material load; therefore, the need existed for a means for further extending the drying time.

According to this invention, a recycling action is obtained by providing a slow relay 130 having a pair of contacts 131 and 132 and a push button switch 133 ganged to the switch 93. Slow return relay 130 has associated therewith a dampening device such as a dash pot 94 to retard the motion of the solenoid armature when moved to the deenergized position. Thus when relay coil 130 is deenergized it may take as long as three seconds to reach the fully open position. One terminal of the relay coil 134 is connected through the switch 133 to the L line terminal 87 while the other terminal of the relay coil 134 is connected to the N line terminal, the coil 134 being thus energized when the switch 133 is closed. When switch 133 is closed, the switch 93 is also closed, and a holding circuit for the relay coil 134 is completed through contact arm 100 and contact 101 of the relay 82 through the contact 131. At the same time, the

relay coil 96 is energized to engage the contactarm 100 with the contact 101, and thus both relays 82 and 130 are maintained energized when the ganged start buttons 93 and 133 are released. The motor 16 and the heater 21 are energized through contacts 81 and 102 respectively in the manner as described above.

As the clothes dry, the resistance of the circuit in shunt with the capacitor 113 increases and ultimately the charge across the capacitor 113 reaches a certain level such as to cause the neon lamp 115 to discharge through the base-emitter circuit of the transistor 116 which then conducts to reduce the voltage of the gate of the rectifier 97, to prevent conduction of the rectifier 97 during the next half-cycle of voltage applied thereto. The relay coil 96 is then momentarily deenergized to open the contacts 81, 101 and 102, and the relay coil 134 is also deenergized through opening of the contact 100 of the relay 82. However, upon deenergization of the slow return recycling relay 130, a contact arm 132 thereof is momentarily (for approximately one second) closed with contact 135 to thus reenergize the relay coil 96 by connecting the relay coil 96 to the L line terminal 87. Accordingly, the motor 16 and the heater 21 are maintained energized through relay contacts 81 and 102 respectively.

The capacitor 113 having been fully discharged as described above through contact 122 of relay 82 again charges up through the resistors 112, 109 and 107 at a rate determined by the resistance of the shunt circuit through the resistors 109 and 107 and the clothes in the dryer. Ultimately, the charge across the capacitor 113 again reaches a certain level such as to cause the neon lamp 115 to discharge through the base-emitter circuit of the transistor 116, and again deenergize the relay 96. At this time, the relay 96 will remain deenergized, since the relay coil 130 is deenergized and the contact 132 is not again momentarily reclosed. The heater 21 is then deenergized, and the motor 16 remains energized until the cool down thermostat opens.

When the recycling relay is used, the time required to charge capacitor 1113 to the firing voltage of the neon lamp 115 can be reduced substantially, in order to obtain a predetermined degree of dryness, since the amount of drying time is increased through the recycling action. This time may be adjusted by adjustment of the resistor 109, and/ or by adjustment of other elements in the circuit. As a result of the recycling action, the operation of the circuit is much more stable and reliable and is not nearly as sensitive to changes in adjustment, operating conditions and parameters of the circuit. In addition, the desired degree of dryness may be obtained automatically despite wide variations in conditions such as the initial moisture content of the clothes, the amount of clothes in the dryer, the type of fabric, ambient temperature and humidity conditions, and the like.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a dryness control circuit for a dryer having heating means and including a dryness measuring and timing circuit arranged to produce a first output signal following a cycle determined by a time dependent on the dryness of the materials being dried,

means responsive to said first output signal for recycling said circuit at least once,

and means responsive to a second output signal from said circuit subsequent to the first output signal therefrom for reactivating said heating means.

2. In a dryness control circuit for a dryer having heating means and including a dryness measuring and timing circuit arranged to produce an output signal following a cycle determined by a time dependent on the dryness of the materials being dried,

a start switch,

a relay in circuit with said switch having a contact for controlling operation of said heating means and holding contact in parallel with said start switch,

means responsive to said output signal for momentarily opening said relay circuit,

means responsive to said output signal for momentarily shorting said start switch to reenergize said relay and recycling said dryness measuring and timing circuit,

means responsive to a second output signal from said circuit produced upon recycling for deactivating said heating means and thereby determining the end of the drying operation.

3. In a dryness control circuit for a dryer having heating means and including a dryness measuring and timing circuit arranged to produce an output signal at a time dependent on the dryness of the materials being dried,

a recycling relay having a contact momentarily closed upon deenergization thereof,

control means for initiating operation of said heating means and said dryness measuring and timing circuit,

4. In a dryness control circuit for a dryer having heating means,

a dryness measuring and timing circuit comprising:

a capacitor, resistance means for charging said capacitor, means providing a current path in shunt with said capacitor for increasing the rate of charge of said capacitor in response to increasing dryness, and means for discharging said capacitor and for producing a first output signal when the charge of said capacitor reaches a certain value, and means responsive to said first output signal for recycling said circuit and determining the termination of the operation of said heating means in response to a second output signal produced during said recycling. 5. In a clothes dryer including a drum supported for rotation to tumble clothes therewithin and electrically controlled means for passing heated air through the drum to dry the clothes,

a dryness measuring and timing circuit comprising:

a capacitor, means including a source of voltage and resistance means for charging said capacitor, contact means in said drum for engaging the clothes, means connecting said contact means in circuit with said capacitor to provide a current path in shunt with said capacitor for increasing the rate of charge of said capacitor in response to increasing dryness, means including a discharge device in parallel with said capacitor for discharging and producing an output signal when the voltage across said capacitor reaches a certain value,

and means responsive to an output signal from said,

circuit subsequent to the first output signal therefrom for deactivating said heating means.

References Cited by the Examiner UNITED STATES PATENTS 3,122,426 2/1964 Horecky 3445 3,180,038 4/1965 Chafee 34-45 3,197,884 8/1965 Smith 3445 FREDERICK L, MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Examiner. 

1. IN A DRYNESS CONTROL CIRCUIT FOR A DRYER HAVING HEATING MEANS AND INCLUDING A DRYNESS MEASURING AND TIMING CIRCUIT ARRANGED TO PRODUCE A FIRST OUTPUT SIGNAL FOLLOWING A CYCLE DETERMINED BY A TIME DEPENDENT ON THE DRYNESS OF THE MATERIALS BEING DRIED, MEANS RESPONSIVE TO SAID FIRST OUTPUT SIGNAL FOR RECYCLING SAID CIRCUIT AT LEAST ONCE, AND MEANS RESPONSIVE TO A SECOND OUTPUT SIGNAL FROM SAID CIRCUIT SUBSEQUENT TO THE FIRST OUTPUT SIGNAL THEREFROM FOR REACTIVATING SAID HEATING MEANS. 